import java.util.Scanner;

/**
 * @Author YuanYuan
 * @Date 2022/4/27
 * @Time 11:29
 */
public class TestDemo {
    public static int singleDog(int[] arr) {
        int ret = 0;
        for (int i = 0; i < arr.length; i++) {
            ret ^= arr[i];
        }
        return ret;
    }
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String str = scanner.nextLine();
        String[] ret1 = str.split(" ");
        int[] arr1 = new int[ret1.length];
        for (int i = 0; i < arr1.length; i++) {
            arr1[i] = Integer.parseInt(ret1[i]);
        }
        System.out.println("可怜的单身狗是："+singleDog(arr1));

    }
}